This invention relates to a series of iodine derivatives of tetrabenazine (3-(2-methylpropyl)-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-benzo[a]quin olizin-2-one, TBZ,1), a monoamine storage-site selective inhibitor, which iodine derivatives are useful as imaging agents for evaluation of the central nervous system (CNS) neuronal system.
Monoamine neuronal systems, i.e., serotonergic, dopaminergic and adrenergic neurotransmitters, have been implicated in various neurological and psychiatric disorders. Different types of therapeutic agents aiming at these neuronal systems, as the pharmacological basis for treatment, are well known. Evaluation of the innervation of these neuronal systems is essential and important for understanding the pathophysiology, and for monitoring progress of patient treatment. New and powerful imaging methods which enable one to assess the living brain in vivo and thereby monitor the effectiveness of drugs and substances that affect brain chemistry have recently been developed. Methods such as positron emission tomography (PET) and single photon emission tomography (SPECT) involve the administration to a patient of radioactive tracer substances comprising a ligand that binds to presynaptic or postsynaptic neuroreceptors in the patient's brain. Emissions (primarily gamma rays which are emitted from the positrons or photons emitted from the radioactive tracer) are measured. These emissions are indicative of the number and degree of occupancy or blocking of the neuroreceptors. The number of neuroreceptors and the degree of occupancy or blocking is calculated utilizing a mathematical model, and compared with an intra-person or inter-person control, to determine the degree of drug response. Further treatment of the patient with drugs can be based upon the comparisons made.
The CNS neuronal systems can take up selective neurotransmitters, such as dopamine, serotonin, norepinephrine etc, from either plasma or from the synaptic cleft. This reuptake process is achieved by a selective transport mechanism based on a specific reuptake receptor on the specific type of presynaptic neuronal terminal. However, once the transmitters are inside the specific type of neuron, a second transporter or reuptake and storage mechanism is responsible for storing and packing the neurotransmitters in vesicles (or granules).
The second transport mechanism, contrary to that for the presynaptic reuptake, is based on a common ATP-dependent transporter which resides on the surface of the vesicles. The second transporters are non-selective and are effective for catecholamines, serotonin and histamine. The neurotransmitters stored in the vesicles are protected from degradation by monoamine oxidases (MAOs) in the cytosol. When neural transmissions are induced by electrical signals, the vesicles in the presynaptic neurons are fused with the membrane and the stored neurotransmitters are released into the synaptic cleft for postsynaptic receptor binding, which leads to further signal transduction.
Reserpine is a natural product which inhibits the monoamine uptake-storage mechanism of amine granules in the synapse. Tetrabenazine, 3-(2-methylpropyl)-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H -benzo[a]quinolizin-2-one (TBZ), ##STR4## is an analog of reserpine which displays a similar biological profile. Due to their ability to deplete monoamines in the CNS, both were used as antipsychotic agents in the 1950's (Cooper J. R., Bloom F. E., Ruth R. H., In Biochemical Basis of Neurochemistry, 5th ed., Oxford University Press, New York, 1986, p. 290; Neumeyer J. L., Neuroleptics and axiolytic agents. In Principles of Medicinal Chemistry, Foye, W. O., ed. Lea and Febiger, Philadelphia, Pa., 1981; Kaiser C., Setler P. E., Antipsychotic agents. Burger's Medicinal Chemistry, 4th Ed. Wolf M. E., ed. Wiley-Interscience, New York, 1981, pp 860-964). The depletion of catecholamines and serotonin in the brain by reserpine is long-lasting and the storage mechanism is irreversibly damaged. Tetrabenazine produces a similar effect; however, the drug effects of TBZ are of a shorter duration and do not cause irreversible damage to neurons (Cooper J. R., Bloom F. E., Ruth R. H., In Biochemical Basis of Neurochemistry, 5th ed., Oxford University Press, New York, 1986, p. 290; Neumeyer J. L., Neuroleptics and axiolytic agents. In Principles of Medicinal Chemistry, Foye, W. O., ed. Lea and Febiger, Philadelphia, Pa., 1981). Clinical studies appear to suggest that treatment of patients with TBZ with up to 300 mg daily improved tardive dyskinesia in several trials (Neumeyer J. L., Neuroleptics and axiolytic agents. In Principles of Medicinal Chemistry, Foye, W. O., ed. Lea and Febiger, Philadelphia, Pa., 1981).
Recently, [.sup.3 H]dihydro-TBZ (2-hydroxy-3-(2-methylpropyl)-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H -benzo[a]quinolizine) has been used as a selective marker for the monoamine transport system in vitro. A detailed review of the use of [.sup.3 H]dihydro-TBZ and [.sup.3 H]reserpine as ligands for in vitro investigation of the monoamine transporter of chromaffin granules and CNS synaptic vesicles was published recently (Henry, J. P., Scherman D., Radioligands of the vesicular monoamine transporter and their use as markers of monoamine storage vesicles (Commentary). Biochem Pharmacol 38:2395-2404, 1989). In vitro binding studies of [.sup.3 H]dihydro-TBZ using membranes of chromaffin granules and brain tissue samples demonstrated a high binding affinity (Kd=2-9 nM) (Darchen F., Masuo Y., Vial M., Rostene W., Scherman D., Quantitative autoradiography of the rat brain vesicular monoamine transporter using the binding of [.sup.3 H]dihydrotetrabenazine and 7-amino-8-[.sup.125 I]iodoketanserin. Neurosci 33:341-349, 1989; Meshgin-Azarian S., Chang W., Cugier D. L., Vincent M. S., Near J. A., Distribution of [.sup.3 H]dihydrotetrabenazine binding in bovine striatal subsynaptic fractions: Enrichment of higher affinity binding in a synaptic vesicle fraction. J. Neurochem 50:824-830, 1988; Near J. A., [.sup.3 H]Dihydrotetrabenazine binding to bovine striatal subsynaptic vesicles. Mol Pharmacol 30:252-257, 1986; Scherman D., Raisman R., Ploska A., Agid Y., [.sup.3 H]Dihydrotetrabenazine, a new in vitro monoaminergic probe for human brain. J. Neurochem 50:1131-1136, 1988; Suchi R., Stern-Bach Y., Gabay T., Schuldiner S. Covalent modification of the amine transporter with N,N'-dicyclohexylcarbodiimide. Biochem 30:6490-6494, 1991).
The regional distribution of the dihydro-TBZ binding sites in brain sections corresponded to the monoamine cell bodies and nerve endings in normal and lesioned brain sections (Masuo Y., Pelaprat D., Scherman D., Rostene W., [.sup.3 H]Dihydro-tetrabenazine, a new marker for the visualization of dopaminergic denervation in the rat stratum. Neurosci Lett 114:45-50, 1990). Various derivatives of TBZ have been reported (Kaiser C., Setler P. E., Antipsychotic agents. Burger's Medicinal Chemistry, 4th Ed. Wolf ME, ed. Wiley-Interscience, New York, 1981, pp 860-964; Neumeyer J. L., Neuroleptics and axiolytic agents. In Principles of Medicinal Chemistry, Foye, W. O. ed. Lea and Febiger, Philadelphia, Pa., 1981; Clarke F. H., Hill R. T., Koo J., Lopano R. M., Maseda M. A., Smith M., Soled S., VonVeh G., Vlattas I. A series of hexahydro[1,4]oxazino[3,4-a]isoquinolines as potential neuroleptics. J. Med. Chem. 21:785-791, 1978; Saner A., Pletscher A. A benzo[a]quinoline derivative with a neuroleptic-like action on cerebral monoamine turnover. J. Pharmacol. Exp. Ther. 203:556-563, 1977; Lednicer D., Mitscher L. A. The Organic Chemistry of Drug Synthesis. Wiley-Interscience Inc., New York, 1977, pp 349-361; Fahrenholtz K. E., Capomaggi A., Lurie M., Goldberg M. W., Kierstead R. W. Octahydrophenanthrene analogs of tetrabenazine J. Med. Chem. 9:304-310, 1967; Harnden M. R., Short J. H. 2-Thiol-1,3,4,6,7,11b-hexahydro-9,10-dimethoxy-2H-benzo[a]quinolizines. J. Med. Chem. 10:1183-1184, 1967; Tretter J. R., U.S. Pat. No. 3,053,845, 1962; Pletscher A., Brossi A., Gey K. F. Benzoquinoline derivatives: A new class of monoamine decreasing drugs with psychotropic action. Rev. Neurobiol. 4:275-302, 1962; Brossi A., Lidlar H., Walter M., Schnider O. 16. Synthesenversuche in der Emetin-Reihe. 1. Mitteilung. 2-Oxo-hydrobenz[a]chiolizine. Helv. Chim. Acta. 41:119-139, 1958). Reduction of the ketone to dihydro-TBZ does not affect the binding affinity. The alkylated alcohol derivatives also displayed high potency. In addition, the acetyl derivative of dihydro-TBZ has also been shown to retain high affinity for the transporter. (Scherman D., Gasnier B., Jaudon P., Henry J. P. Hydrophobicity of the tetrabenazine-binding site of the chromaffin granule monoamine transporter. Mol. Pharmacol. 33:72-77, 1988).
The determination of neuronal integrity can be important in differential diagnosis of CNS diseases. An imaging agent for PET and SPECT, which could be useful for evaluation of the presynaptic neuronal functions, especially the uptake and storage mechanism, could serve the need of a large population of patients receiving drug treatments targeting the monoamine neurons.